Generally, a swash plate type variable displacement hydraulic rotary machine which is provided on a construction machine like a hydraulic excavator is used as a variable displacement hydraulic pump which constitutes a hydraulic pressure source along with a tank, or as a variable displacement hydraulic motor which constitutes a hydraulic actuator for driving a vehicle or for revolving a working mechanism of the machine.
According to prior art, for example, a swash plate type variable displacement hydraulic rotary machine is composed of a swash plate which is tiltably provided within a casing to serve as a variable displacement member, a tilting actuator provided within the casing and equipped with a servo piston for driving the swash plate into a tilted position according to a tilting control pressure which is supplied from outside, a regulator in the form of a servo valve provided within the casing and having a spool within a control sleeve for variably controlling the tilting control pressure to the tilting actuator, and a feedback link provided between the control sleeve of the regulator and the servo piston to transmit a displacement of the servo piston to said control sleeve (e.g., Japanese Patent Laid-Open No. 2003-74460).
In this instance, the above-mentioned feedback link is in the form of a bifurcated holder spring with a function of attenuating high frequency vibrations. This holder spring is arranged to hold a pin member on the servo piston radially from opposite sides, for picking up and transmitting a displacement of the servo piston to the outside (to the control sleeve of the regulator).
In the case of the prior art mentioned above, the feedback link is constituted by a bifurcated holder spring. Therefore, in this case there is an advantage that, in the event the swash plate is put in repeated high frequency vibrations under the influence of pulsations in hydraulic pressure, high frequency vibrations can be attenuated by the holder spring portion of the feedback link as high frequency vibrations are transmitted to the servo piston from the swash plate.
The holder spring of the above-mentioned prior art is constituted by a pair of (a couple of) holder portions which are adapted to hold a pin member on the servo piston radially from opposite sides, to pick up and transmit an axial displacement of the servo piston to the outside through the two holder portions. However, the holder spring by the prior art suffers from problems as discussed below.
More specifically, the tilting actuator drives the swash plate into a tilted position by displacing the servo piston in the axial direction. Therefore, at the time of changing the tilt angle of the swash plate, each time the servo piston is displaced axially in a forward or reverse direction.
However, as the direction of axial displacement of the servo piston is reversed, one of the two holder portions which are provided on the holder spring, more specifically, one holder portion which is located in a rear side in the direction of displacement of the servo piston is slightly moved away from the surface of the pin member even if the other holder portion (which is located in a front side in the direction of displacement) is held in abutting engagement with the pin member. This gives rise to a problem that a rattling movement takes place between the pin member and a pair of holder portions each time the direction of displacement of the servo piston is reversed.
When the control of the tilt angle of the swash plate (displacement control) is repeated during use over an extended period of time, impact load attributable to the rattling movement is repeatedly applied to the holder spring to cause plastic deformation of the latter. If the holder spring undergoes deformations repeatedly in this manner, it becomes difficult for the holder spring (for the feedback link) to pick up and transmit displacements of the servo piston to the outside in a stable state.